Mr. Mark Welton

apprehensiveheehawNetworking and Communications

Oct 26, 2013 (3 years and 10 months ago)

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Mr. Mark
Welton


A
computer network
, or simply a
network
, is a
collection of computers and other hardware
interconnected by communication channels that
allow sharing of resources and information
.
Where at least one process in one device is able
to send/receive data to/from at least one process
residing in a remote device, then the two devices
are said to be in a network. A network is a group
of devices connected to each other. Networks
may be classified into a wide variety of
characteristics, such as the medium used to
transport the data, communications protocol
used, scale, topology, benefit, and organizational
scope
.
-

Wikipedia


A computer network can be defined as two or more
computers connected by some means through which they are
capable of sharing information


So is sneaker net a network?





A connection involves some sort of
addressing or identification of the nodes on
the network, allowing them to speak the
same protocol or language
.


Types of networks:


LAN
-

is a network that is confined to a limited
space, such as a building or floor
.


WAN
-

A WAN is a network that is used to
connect LANs by way of a third
-
party provider
.


CAN
-

is a network that connects LANs and/or
buildings in a discrete area owned


or controlled by a single entity
.


MAN
-

is a network that connects LANs and/or
buildings in an area that is often


larger than a campus.


We also describe networks by the technology they use


Ethernet


Token Ring


FDDI (Fiber
Distributed Data Interface
)


Or the Protocols:


ATM


Frame Relay


MPLS


T1


DS3


Or the layer:


Bridged


Routed


Point
-
to
-
point




Early Ethernet, 10Base
-
5 used a thick cable
named
thick
-
net


10Base
-
2
Ethernet replaced 10Base
-
5 and
used a smaller coaxial cable named
thin
-
net



Both used either an N or BNC connector to
couple cables together and required
terminators to be installed at the end of a
cable
run


These
cable runs formed the physical
backbone of Ethernet
networks




Ethernet running over UTP cables terminated
with RJ45 connectors made use of
hubs


Hubs
became the new backbone of many
installations


As hubs became less expensive, extra hubs
were often used a repeaters in more complex
networks


Hubs are layer one devices (physical/electrical
devices) and do not alter frames or make
decisions on traffic it
sees


A
hub
is simply a means of connecting
Ethernet cables together so that their signals
can be
repeated to every other connected
cable on the
hub


Hubs may also be called
repeaters
for
this
reason, but it is important to understand that
while a hub is a
repeater, a
repeater is not
necessarily a hub.


If another device is already using the wire, the
sending device will wait a bit and
then try
to
transmit
again


When
two stations transmit at the same time,
a
collision
occurs


Each station records the collision, backs off
again, and then
retransmits


A collision domain is an area


of an Ethernet network where collisions can
occur


A
broadcast domain
is the area of an Ethernet
network where a broadcast will be
propagated


Broadcasts stay within a Layer
-
3 network
(unless forwarded), which is
usually bordered
by a Layer
-
3 device such as a
router


A broadcast storm results in the attempt to
build redundancy into the
network


The
only way to resolve a broadcast storm is
to break the
loop


The
5
-
4
-
3 rule
of Ethernet design states that
between any two nodes on an Ethernet
network, there
can be only five segments,
connected via four repeaters, and only three
of
the segments
can be populated. This rule,
which seems odd in the context of today’s
networks, was
the source of much pain for
those who didn’t understand it.


Switches differ
from hubs by
playing an active
role in the processing of frames on the
network


Switch
-

The general term used for anything
that can
switch


Ethernet S
witch
-

Any device that forwards
frames based on their Layer
-
2 MAC
addresses
using Ethernet


A switch creates a collision domain on each
port, while a hub’s collision domain exists on
all
ports


Layer
-
3 S
witch
-

This is a switch with routing
capabilities


Multilayer S
witch
-

Similar to a Layer
-
3
switch, but may also allow for control based
on higher
layers in
packets. Multilayer
switches allow for control based on TCP, UDP,
and
even details
contained within the data
payload of a
packet


Switching
-

is the act of forwarding frames
based on their destination MAC
addresses


Every frame contains the source and destination MAC
address


switch inspects the frame to determine the source MAC address and
adds the address into its address
table


The switch then determines the frame’s destination MAC address and
checks the
table


If a match exists, the frame is forwarded from the source port to the
destination port. If no match is found, the frame is sent to all
ports


Routing
-

refers
to determining the path for
something


For IP, packets and frames are forwarded by
switches and
hubs


To
reach a destination, not on the local
network, the packet must be forwarded to a
gateway


The
gateway (router) is responsible for
determining how to get the packet to where it
needs to go



Routers communicate with each other by
routing
protocols


These
protocols let the routers learn
information about other
networks
which are
stored in the routing table of the
router


With the introduction of layer three switches


routers tend to remain WAN
-
focused, while
switches remain
LAN
-
focused


Routing is a fundamental process common to
almost every
network


Each routing protocol has its own table of
information (learned through its own protocol


in addition to the routing table of the router
)


Metrics
-

the values or weight used by a routing
protocol to determine its best path to a
destination


Administrative distance is the values assigned to
each routing protocol by the router in order to
prioritize learned routes


I
f
the same route is learned from two sources
within a single routing protocol, the one with
the best metric will
win


If the
same route be learned from two routing
protocols within a single router, the protocol
with the lowest administrative distance will be
preferred


When a packet arrives at a router, the router
determines whether the packet needs to be
forwarded to another
network


If it does, the router checks the routing table to
determine if it contains a route to the destination
network


If
there is a match, the packet is forwarded out
the proper interface to where it
belongs


If there is no match found in the routing table,
the packet is forwarded to the default gateway, if
one exists, or dropped if no default gateway
exists


IP destination networks are often described
by a network address and prefix
length


The prefix length is the number of bits set to
1 in the subnet
mask


Networks are described in the format
network
-
address/prefix
-
length


i.e. 10.0.0.0/16


referred to as a prefix


10.0.0.0/24


10.0.0.0/16


10.0.0.0/8


Which has the longer prefix?


A longer prefix means a more specific match
to a
destination


Host route


subnet route


summary route


major
network
route


supernet

route


default
route


Host route is a route to a host (node), not a
network


Host routes have a subnet mask of
255.255.255.255 or a /32
prefix


The
subnet mask is all 1s


Subnet route is a portion of a major
network


The subnet mask is used to determine the
network


24 is a subnet of the
classful

10.0.0.0
network


Subnets make use of Variable Length Subnet
Masks of
classful

major
networks


Summary route is a single route that
references a group of
subnets


10.1.0.0/16 would be a summary route for
the subnet routes of 10.1.1.0/24 and
10.1.2.0/24



is any
classful

network with its traditional
subnet
mask


Class A, B, C
networks


Supernet

route is a single route that
references a group of major
network


192.168.0.0.0/15 is a
supernet

for
192.168.0.0.0/16 and
192.169.0.0/16


Default route is the gateway (route) of last
resort


typically shown as 0.0.0.0 (an all zero)
destination


The subnet mask is all
zeroes